In a papermaking machine, devices are frequently employed for pressing a running fibrous web for various purposes. For example, in a press section of a papermaking machine, shoe presses are commonly used for pressing the web so as to remove water from the relatively wet web coming from the forming section of the machine. As another example, calendering of a web is frequently performed in a nip of a calender device for imparting desired surface characteristics to the web.
Shoe presses generally comprise a press shoe and a counter roll, which components form an extended nip between themselves for treating (e.g., dewatering when the shoe press is used in the press section of a paper or board machine) a paper or cardboard web. Furthermore shoe presses generally have pressurizable piston-and-cylinder units or loading cylinders which are distributed along the press shoe in one or more rows in the longitudinal direction of the press shoe and are operable for urging the press shoe toward the counter roll, see e.g. EP 345 501 B2, DE-195 15 832 C1, and DE 44 09 316 C1.
Sometimes shoe presses also comprise compartments which are formed in the upper surface facing the counter roll and which, in operation, contain fluid under hydrostatic pressure for lubricating the belt, see e.g. EP-345 501 B2. Such compartments are often called hydrostatic compartments or pockets.
Furthermore shoe presses may comprise a hydrostatic compartment or pressure chamber between each loading cylinder and the press shoe and which in operation contains fluid under hydrostatic pressure. The pressure chamber reduces sliding friction between the press shoe and loading cylinder surfaces such that the press shoe can more easily slide relative to the loading cylinders, see e.g. DE 195 15 832 C1.
The above-mentioned loading cylinders, compartments, and chambers thus require access to hydraulic fluid. The compartment for hydrostatic pressure according to EP-345 501 B2 is pressurized by hydraulic fluid through a duct which is horizontally bored in the longitudinal direction of the shoe press in the frame system of the shoe press and which is shared by all the compartments. Furthermore, in the shoe press disclosed in EP-345 501 B2, the working chambers of the loading cylinders are also pressurized by hydraulic fluid via ducts bored in the frame system of the shoe press. Similarly, DE 195 15 832 C1 also discloses a shoe press having ducts which are bored in the frame system of the shoe press and which are adapted to supply hydraulic fluid to the loading cylinders and as well as to pressure chambers between the press shoe and the loading cylinders. The working chambers of the loading cylinders are connected to the pressure chambers via throttles formed through the cylinder members of the loading cylinders.
Thus, in prior shoe presses, supply of fluid to the loading cylinders and/or hydrostatic compartments between the loading cylinders and the press shoe is accomplished via ducts formed in the frame systems of the shoe presses. The frame system of a shoe press typically is formed of steel beams, and accordingly, boring ducts through the frame system is a complicated and expensive procedure. Moreover, the bored ducts are of fixed geometry and thus are invariable and unalterable. There thus is a need of simplifying and making the supply of hydraulic fluid to the hydrostatic compartments, pressure chambers, and loading cylinders less expensive.
In the shoe press disclosed in DE 195 14 142 C1, there is a spring in the working chamber of the loading cylinder for sealingly pressing the loading cylinder against the press shoe and preventing hydraulic fluid from escaping sideways from the pressure chamber formed between the loading cylinder and the press shoe. The shoe press also has a number of tie-rod-spring arrangements which in pairs engage the press shoe on the longitudinal sides between the loading cylinders and which are operable for limiting the distance by which the press shoe can be moved away from the frame in the direction of the counter roll. The tie-rod-spring arrangements take up a considerable amount of space. There thus is also a need for a mechanism for limiting the movement or stroke of a press shoe which mechanism requires less space.